[Fix #9122] Added notification if any gems are loaded that have rubocop extensions.

.rubocop.yml

@@ -15,6 +15,7 @@ AllCops:
     - '.git/**/*'
     - 'bin/*'
   TargetRubyVersion: 2.4
+  SuggestExtensions: false
 
 Naming/PredicateName:
   # Method define macros for dynamically generated method.

changelog/change_added_notification_if_any_gems_are.md

@@ -0,0 +1 @@
+* [#9122](https://github.com/rubocop-hq/rubocop/issues/9122): Added tip message if any gems are loaded that have RuboCop extensions. ([@dvandersluis][])

config/default.yml

@@ -139,6 +139,16 @@ AllCops:
   # from the lock file.) If the Ruby version is still unresolved, RuboCop will
   # use the oldest officially supported Ruby version (currently Ruby 2.4).
   TargetRubyVersion: ~
+  # Determines if a notification for extension libraries should be shown when
+  # rubocop is run. Keys are the name of the extension, and values are an array
+  # of gems in the Gemfile that the extension is suggested for, if not already
+  # included.
+  SuggestExtensions:
+    rubocop-rails: [rails]
+    rubocop-rspec: [rspec, rspec-rails]
+    rubocop-minitest: [minitest]
+    rubocop-sequel: [sequel]
+    rubocop-rake: [rake]
 
 #################### Bundler ###############################
 

lib/rubocop.rb

@@ -648,6 +648,7 @@
 require_relative 'rubocop/cli/command/execute_runner'
 require_relative 'rubocop/cli/command/init_dotfile'
 require_relative 'rubocop/cli/command/show_cops'
+require_relative 'rubocop/cli/command/suggest_extensions'
 require_relative 'rubocop/cli/command/version'
 require_relative 'rubocop/config_regeneration'
 require_relative 'rubocop/options'

lib/rubocop/cli.rb

@@ -69,10 +69,14 @@ def execute_runners
       if @options[:auto_gen_config]
         run_command(:auto_gen_config)
       else
-        run_command(:execute_runner)
+        run_command(:execute_runner).tap { suggest_extensions }
       end
     end
 
+    def suggest_extensions
+      run_command(:suggest_extensions)
+    end
+
     def validate_options_vs_config
       if @options[:parallel] &&
          !@config_store.for_pwd.for_all_cops['UseCache']

lib/rubocop/cli/command/suggest_extensions.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+module RuboCop
+  class CLI
+    module Command
+      # Run all the selected cops and report the result.
+      # @api private
+      class SuggestExtensions < Base
+        # Combination of short and long formatter names.
+        INCLUDED_FORMATTERS = %w[p progress fu fuubar pa pacman].freeze
+
+        self.command_name = :suggest_extensions
+
+        def run
+          return if skip? || extensions.none?
+
+          puts
+          puts 'Tip: Based on detected gems, the following '\
+            'RuboCop extension libraries might be helpful:'
+
+          extensions.each do |extension|
+            puts "  * #{extension} (http://github.com/rubocop-hq/#{extension})"
+          end
+
+          puts
+          puts 'You can opt out of this message by adding the following to your config:'
+          puts '  AllCops:'
+          puts '    SuggestExtensions: false'
+          puts if @options[:display_time]
+        end
+
+        private
+
+        def skip?
+          # Disable outputting the notification:
+          # 1. On CI
+          # 2. When given RuboCop options that it doesn't make sense for
+          # 3. For all formatters except specified in `INCLUDED_FORMATTERS'`
+          ENV['CI'] ||
+            @options[:only] || @options[:debug] || @options[:list_target_files] || @options[:out] ||
+            !INCLUDED_FORMATTERS.include?(current_formatter)
+        end
+
+        def current_formatter
+          @options[:format] || @config_store.for_pwd.for_all_cops['DefaultFormatter'] || 'p'
+        end
+
+        def extensions
+          extensions = @config_store.for_pwd.for_all_cops['SuggestExtensions']
+          return [] unless extensions
+
+          extensions.select { |_, v| (v & dependent_gems).any? }.keys - dependent_gems
+        end
+
+        def dependent_gems
+          # This only includes gems in Gemfile, not in lockfile
+          Bundler.load.dependencies.map(&:name)
+        end
+
+        def puts(*args)
+          output = (@options[:stderr] ? $stderr : $stdout)
+          output.puts(*args)
+        end
+      end
+    end
+  end
+end

lib/rubocop/config_loader_resolver.rb

@@ -92,7 +92,7 @@ def merge(base_hash, derived_hash, **opts)
       keys_appearing_in_both.each do |key|
         if opts[:unset_nil] && derived_hash[key].nil?
           result.delete(key)
-        elsif base_hash[key].is_a?(Hash)
+        elsif merge_hashes?(base_hash, derived_hash, key)
           result[key] = merge(base_hash[key], derived_hash[key], **opts)
         elsif should_union?(base_hash, key, opts[:inherit_mode])
           result[key] = base_hash[key] | derived_hash[key]
@@ -164,6 +164,10 @@ def should_union?(base_hash, key, inherit_mode)
         inherit_mode['merge'].include?(key)
     end
 
+    def merge_hashes?(base_hash, derived_hash, key)
+      base_hash[key].is_a?(Hash) && derived_hash[key].is_a?(Hash)
+    end
+
     def base_configs(path, inherit_from, file)
       configs = Array(inherit_from).compact.map do |f|
         ConfigLoader.load_file(inherited_file(path, f, file))

spec/rubocop/cli/cli_autocorrect_spec.rb

@@ -7,6 +7,7 @@
 
   before do
     RuboCop::ConfigLoader.default_configuration = nil
+    RuboCop::ConfigLoader.default_configuration.for_all_cops['SuggestExtensions'] = false
   end
 
   it 'does not correct ExtraSpacing in a hash that would be changed back' do

spec/rubocop/cli/cli_options_spec.rb

@@ -766,6 +766,10 @@ class SomeCop < Cop
   end
 
   describe '-d/--debug' do
+    before do
+      RuboCop::ConfigLoader.default_configuration = nil
+    end
+
     it 'shows config files' do
       create_file('example1.rb', "\tputs 0")
       expect(cli.run(['--debug', 'example1.rb'])).to eq(1)